Dual aerating apparatus and method



July 19, 1955 A, C, DAMAN 2,713,477

DUAL AERATING APPARATUS AND METHOD Filed April '7, 1952 4 Sheets-Sheet l INVENTOR. Arthur C. Dumon July 19, 1955 A. c. DAMAN DUAL AERATING APPARATUS AND METHOD Filed April 7, 1952 4 Sheets-Sheet 2 FlG.-7

INVENTOR. Arrhur' C. Damon ATTORNEY July l9, 1955 A. c. DAMAN 2,713,477

DUAL AERATING APPARATUS AND METHOD Filed April '7, 1952 4 Sheec-Sheet 5 Arhur C. Domun ATTORNEY DUAL AERATING APPARATUS AND METHOD Filed April 7, 1952 4 Sheets-Sheet 4 INVENTOR. Arthur C. Dumon Md MMA ATTORNEY Unted States Patent "l" DUAL AERATL\TG APPARATUS AND METHOD Arthur C. Daman, Denver, Coto., assigner to Mining Process and Patent Company, Denver, Colo., a corpon ration of Delaware Appiication April 7, 1952, Serial No. 280,970

19 Claims. (Cl. 261-87) This invention relates to methods and apparatus for aeration and more particularly relates to aeration treatments of the type performed in froth flotation treatments and similar operations.

ln the past it has been customary to employ a single rotary impeller in froth flotation apparatus which performs the dual function of an aerator and an agitator or pump. The impeller has to provide the necessary pumping action for circulation of the pulp through the cell and from cell to cell. In addition it has to provide the necessary mixing of reagent, pulp and air or other aerating media to attain the desired aeration effect to cause the mineral to carry to the surface.

More recently it has been conventional in froth flotation treatments to provide rotary impellers encompassed or enclosed within a surrounding structure which serves to break up discharging pulp and thereby provide a greater degree of diffusion of the air being mixed with the pulp. Such arrangements have had the advantage of restraining the intense agitation produced by high speed rotation of the impeller and have permitted reagents to be used which have a more selective action on the mineral being collected and which are not so tenacious and break down more readily in the subsequent treatment. These arrangements usually take the form of a stationary enclosure having suitable apertures or openings through which pulp will be discharged.

One defect of all of these arrangements is that the impeller has to provide the necessary rate of rotation to perform the circulatory or pumping function and thereby induces such a high speed movement of circulating pulp that it interferes with the action of the flotation reagent carrying mineral to the froth bed at the surface. In order to control this over circulation or agitation, Various mechanical expedients have been resorted to in the past, such as baiiles, grids and the like, which tend to break down the movement and produce a more gentle aerating effect in the upper part of the cell. However, even when so restrained, the action is not entirely satisfactory as the aeration function is actually secondary to the pumping function in any such arrangement. Other arrangements have involved the use of upper and lower impeller members in the same cell, the lowermost impeller being operated primarily as a pump to produce the necessary circulation, while the upper impeller operates primarily as an aerator to mix and diffuse the pulp and air or other aerating gas.

While various arrangements of the prior art have been satisfactory for their intended purpose, none of the machines so far developed have stood the test of being an all purpose unit for various types of treatment. The present invention represents a departure from prior practice in that it provides a pumping or circulatory unit in the lower part of the cell which also has an apertured enclosure which serves to break up the discharging pulp stream and produces a more intense aeration and a reduction in the circulatory movement outside of the agitation zone. ln addition, the upper part of the cell preferably 2,ii37? Patented `Fully i9, 1S55 the aerating function of froth flotation treatments or the' like, in which pulp in the lower portion of the treatment Zone is subjected to sufficient agitation and mixing to produce the desired circulatory effect, both within the cell and from said cell to another succeeding cell or other reatment unit, while the zone of pulp above the first treatment stage has a second aerating unit which serves to mix pulp and air and induce the necessary elevating movement of the filmed mineral to collect in the froth at the surface.

Another object of the invention is to provide simple, durable and efficient aerating apparatus which is designed to provide the desired degree of circulation of material through the cell and at the same time produces an intense and highly diffused aeration of pulp within said cell.

A further object of the invention is to provide simple, durable and efficient froth iiotation apparatus which is adapted to produce a selective degree of aeration at various zones within the body of pulp under treatment.

Other objects reside in novel details of construction and novel combinations and arrangements of parts, all of which will be described more fully in the course of the following description.

With this understanding of the objects and purposes of the present invention, the practice of the invention will be best understood by reference to the accompanying drawings. In the drawings in the several views of which like parts are designated similarly,

Fig. 1 is a front elevation partially broken away to show the interior arrangement of a Z-cell unit embodying the aerating features of the present invention;

Fig. 2 is an end elevation partially broken away to show the interior arrangement of parts of the unit shown in Fig. l;

Fig. 3 is a front elevation of a 2-cell aerating unit partially broken away to show the arrangement of interior parts and embodying another modification of the aerating features of the present invention;

Fig. 4 is a front elevation of a 2-cell unit partially broken away to show the arrangement of interior parts of still another modification of the cell arrangement embodying features of the present invention;

Fig. 5 is a fragmentary front elevation of one of the aerating units utilized in the practice of the present invention;

Fig. 6 is a front elevation of a modified form of aerating unit utilized in the present invention;

Fig. 7 is a front elevation of a third form of aerating unit practiced in the present invention;

Fig. 8 is a top plan view of the aerating unit shown in Fig. 5;

Fig. 9 is a top plan view of the aerating unit shown in Fig. 6 and;.

Fig. 10 is a top plan view of the aerating unit shown in Fig. 7.

In the form of the invention shown in Figs. l and 2, the tank T, comprising two cells C and C', is provided with a bottom 11, front wall 12, rear wall 13 and end l walls 14 and 15. Suitable superstructure 16 is located on the top walls of the tank and supports a motor 17 and shafts 18 and 18a, suitably journaled in bearing housings 19 with the ends of the shaft driven through the intermediary of suitable transmission 21 from the motor 17. Tank T has a feed inlet 22 which may extend nteriorly of the cell to a central point of discharge or may terminate in close proximity to the end wall 14. Similarly, a discharge outlet 23 is located adjacent or in end wall 15 and provides the final discharge from the machine. While only a 2-cell arrangement has been shown, it will be understood that any suitable number of intermediate cells may be provided, which except for the feed and discharge features, are essentially the same as cells C and C.

The discharge through the outlet 23 is under the control of a weir 24 regulated as to effective overflow level by hand wheel controlled gate 25. The cells are provided with a froth overflow lip 26 extending along the front wall 12 and when desired a similar overflow lip 26a is provided for the rear wall 13. Suitable scrapers, such as scraper 27 shown in Fig. l, are provided for movement of froth across said overflow lips. The aerating gas, usually air, is supplied through a suitable header 28 from which it enters a branch 29 delivering gas to the hollow interior of the bearing housing. Each of said housings is provided with a slot or aperture 29a which delivers the aerating gas under the control of a valve 31 into other slots 32 in the shaft within the bearing housing. A hollow column 33 is mounted in encompassing relation to the shaft and is supported from a anged connection 34 at `the end of the bearing housing. The lower end of the column supports a hood or cover 35 carrying vanes 36 which surround a rotary impeller 37 carried on the shaft.

Another branch 38 connects the header 28 with the interior of the hollow column 33 and is under the control of a valve 39 to provide a selective degree of aeration into the hollow zone above the impeller. The column is also provided with suitable openings 41 just above its point of attachment to the hood, which permit the entry of circulating pulp from the cell into the zone of treatment of the impeller. Preferably, vanes 42 are located on the under surface of the impeller 37 and provide a sweeping movement of material located immediately under the impeller during its rotation. Below the impeller 37 an annular enclosure E is mounted and consists of a series of bars or rods 43 supported from the bottom of the cell by suitable structure and extending to a point spaced from but in proximity to the under surface of the impeller 37. This enclosure surrounds a bottom rotor R mounted on the shaft and comprising an upper disk 44, a lower disk 45 and a series of interconnecting bars or blades 46 arranged in annular formation with spaces between adjoining bars.

The shaft is provided with laterally extending openings 47 within the enclosure formed by the blades or bars 46 and discharges gas delivered under control of the valve 31 through the slotted openings 32 into said aeration zone in order to mix with pulp fed into said enclosure. The bottom disk of the rotor R is spaced a substantial distance above the bottom of the tank and provides a zone for entrance of pulp delivered into the cell by the feed conduit or pulp delivered from a preceding cell into a succeeding cell in the series such as the cell C. The bottom disk has an opening 49 in its central portion and the upper disk has a similar central opening 51 thus permitting pulp to circulate freely into the enclosure from beneath and above under its pumping influence.

It is sometimes desirable to vary the spacing between the impeller 37 and its hood and also to change the effective elevation of the rotor R within the cell. To this end the bearing housing 19 is supported on an adjustment plate or device 52 to change the elevation of the shaft in the cell and a similar adjustment plate or device 53 is provided for selectively changing the position of the hood overhanging impeller 37.

With this understanding of the construction and arrangement of parts shown in Figs. l and 2, the operation of the unit will now be described. Pulp is fed through the inlet 2.2 and enters cell C to circulate within the pulp body already established in said cell. Most of this pulp will pass to the bottom and enters the space 48 to pass through the opening 49 in the bottom disk and thus enters the interior space of rotor R. At the same time other pulp pushed downwardly and circulated by the vanes 42 on the bottom of impeller l37 descends through the top opening 51 of the upper disk of rotor R and also enters said enclosure. The two streams-are immediately subjected to the centrifugal effect of the rotation of the rotor and move outwardly to strike the bars 46 and penctrate through the spaces between said bars.

While this action is progressing, air is being fed through the shaft and discharges from the lateral outlet 47 to intermingle with the two streams of pulp tending to converge within the opening, and all of the pulp and air streams are substantially intermixed in the initial contact and are brought into further intermingling relation by their contact with the bars 46. After discharging through thc spaces between said bars the pulp is subjected to additional beating and further diffusion of the air is effected in its passage through the bars of the enclosure E.

After passing from the enclosure E, mineral particles which are sufficiently aerated and coated to carry to the surface, travel through the pulp body under the impelling influence of the aeration and thus reach the surface. However, some of the particles, while tending to float, are not suiciently treated to enter the froth bed at the surface and tend to establish a high density zone immediately under the froth bed. The upper impeller serves to prevent such build-up of high density material by drawing off the unoated portions through the openings 41 and into the treatment zone of the upper impeller.

In this zone, the pulp is subjected to additional mixing with air and the air-pulp intermixture is broken up by the action of the blades on the impeller 37 and also by the vanes 36. The additional aeration and mixing thus derived imparts suflicient flotation effect to the mineral brought within the zone of treatment of impeller 37 to cause the discharging mineral to rise readily into the pulp and thus be removed from the treatment.

After being so treated in cell C the pulp moving under the circulatory influence of the rotor R tends to pass into cell C and in order to prevent undue turbulence within cell C a partition 54, preferably located at a substantial incline, with its lower edge adjacent enclosure E is disposed to extend into the upper zone of cell C. Pulp not rising readily in cell C passes under this partition and thus enters the space 4S to pass into rotor R, whereas pulp in substantial suspension or tending to oat will travel across the upper surface of the partition and due to the elevating effect of the discharge of rotor R tends to pass into the froth bed, or failing to do so, is drawn into the impeller 37 of cell C', or is elevated into the froth by the buoyant effect of the aerated discharge of said impeller.

In some treatments it may be desirable to provide further restraint to the circulating pulp entering a succeeding cell from the preceding cell. As illustrated in cell C', I prefer to locate a partition member 55 immediately under rotor R and extending substantially from the front wall 12 to the rear wall 13 of such cell. This partition serves to direct the incoming pulp directly into the interior of rotor R through its bottom opening 49, where it is subjected to the mixing action previously described. It is sometimes desirable to use one or more of such cells for the treatment of a froth concentrate collected in a second cell of the series. To this end, I prefer to locate a return feed conduit on the front wall 12 of the cell at the approximate elevation of rotor R and this opening or coupling may be used to connect a suitable conduit for the return of such concentrate. Also in some treatments or under certain conditions it will be necessary to drain the cells and I provide a suitable drain opening 57 on the rear wall 13 for this purpose.

The form of the invention shown in Fig. 3 is substantially the same as that previously described with differences in the aerating function of the machine. AS shown the machine comprises a tank T consisting of cells Ca and Cb, which as previously described, may be any plurality other than the two cells shown.` The machine has a front wall 62, a rear wall (not shown) and end walls 64 and 65. Suitable superstructure 66 is mounted on the top walls of the cell or tank and carries a motor 67, shaft 68 and 68a, journaled in suitable bearings 69 with transmission '71 actuating the shafts under the driving influence of the motor. The tank has the usual feed inlet 72 and a discharge outlet 73 under the control of a Weir 74 regulated by the gate member 75. Preferably, a front overflow lip 76 and a rear overflow lip (not shown) are provided, although in some treatments the single overflow lip 76 will be adequate. In any event some means is provided for removal of froth across the lip, such as the rotary scraper member 77.

Air is provided by a header 78 and a branch 79 under control of a valve 81 which delivers the air through slots 82 in the shaft for delivery through its hollow interior into the aerating zone of the cell. The shaft in the upper portion of the cell is encompassed by a hollow housing or closure member suspended from the bearing housing by a structure 83 having flanged connection 84 with the bearing housing and including a partition member 85 which divides a double impeller unit located in the upper portion of the cell Ca. The impeller unit comprises a top impeller 86 and a bottom impeller 87 mounted on the shaft and having their adjoining surfaces in spaced but close proximity to their partition S5. The upper impeller S6 is substantially the same impeller structure as the impeller 87 except that it is inverted and provided with a series of openings 88 through its top surface and other openings 89 are provided in the shaft to discharge aerating gas within the enclosure formed by said impellers and the partition S5.

Similarly other openings 89 in the shaft discharge aerating gas into the enclosure formed by the lower impeller member 87 and the partition 85. Each of said impellers is provided with a series of radially disposed blades 91 which serve to impart impelling movement to the pulp and gas and also break up the pulp gas mixture prior to its discharge across the periphery of the respective impellcrs.

An annular enclosure E', similar to the enclosure E of Fig. 1, is supported from the bottom of the cells Cl and Cb and preferably comprises a series of upstanding bars or rods 93. A rotor R' is mounted at the lower end of the shaft within the enclosure E and preferably comprises an upper disk 94, a lower disk 95, and a series of peripherally spaced blades or bars interconnecting said disks. As in the former arrangement laterally extending openings 97 in the shaft discharge aerating gas within the enclosure formed by the respective disks of the rotor and provide the necessary aerating action in its rotation.

With this understanding of the structural arrangement comprising the form of the invention shown in Fig. 3, its action will now be described. Pulp entering through the inlet '72 descends into the lower Zone of cell Ca and is drawn into the space 98 underneath the rotor R. This pulp passes upwardly through the central opening 99 in the bottom disk 95 and within the enclosure of the rotor mingles with other pulp descend ing through the top opening 161 of upper disk 94. The pulp is aerated by the introduction of gas through the openings in the shaft within the enclosure and this aerated pulp first strikes the bars 93 of the rotor and then passes into a second Zone where it is subjected to a further beating action before passing through the spaces between the bars in the enclosure E.

As in the former operation, the pulp not readily suspended or freely floating, passes underneath an inclined baffle member 104 to enter the cell Cb, while the susfit) 6 pended pulp or pulp tending to float travels across the baille or partition 104 into cell C`D and it descends along the upper surface of said partition.

After the pulp passes from the enclosure E, the aerated mineral travels to the surface in the manner previously described, and mineral tending to float but not carrying into the froth at the surface, is drawn into the upper impeller structure by the action of the aerating impellers, particularly the upper impeller, exerting a suction intluence through the provision of the holes 88 in its top surface. The pulp is thereby subjected to further aeration and mixing and upon discharge across the periphery in proximity to partition is in proper condition for the flotation separation. Froth collecting at the surface discharges across the overflow lip and the circulation induced by the rotation causes other pulp to pass from cell Ca into cell Cb where the previously described action is repeated. Again in this form of the invention l prefer to have a partition member 105 located underneath the rotor R in order to restrain agitation and to insure delivery of a steady feed to the rotor.

The form of the invention shown in Fig. 4 differs somewhat from the forms previously described in that only a single impeller unit is provided, although said unit is divided into upper and lower sections which function in the manner of independent impeller units. As shown in Fig. 4, the impeller structure may comprise the form of two rotary sections divided by a stationary partitioning member, or as shown in cell Cy of Fig. 4, the impeller may comprise a single rotor divided by a suitable partition into upper and lower chambers.

With this understanding of the differences in structural arrangement, the other features of the structure shown in Fig. 4 will now be set forth. This unit also comprises a tank T comprising cells CX and CY, inclusive of a front wall 112, a rear wall (not shown), end walls 114 and 115, and a bottom 111. A suitable superstructure 116 is mounted on the top of the cell structure and carries a motor 117, shafts 118 and 113a journaled in bearings 119 and driven by the motor through the intermediary of transmission 121. This tank also has the usual feed inlet 122 and discharge outlet 123 controlled by a Weir 124 under the actuation of a gate mechanism 125. As in the other forms of the invention the respective cells are provided with a front overiow lip 126 and, if desired, a rear overflow lip (not shown) with froth removal effected by Scrapers 127.

Air or other aerating gas is delivered into the cells from a header 123 by a branch 129 under control of a valve 131 and enters the slots 132 in the shaft to descenrl through the shaft and into the aerating Zone. In the upper portion of the cell, the shaft is encompassed by a column 133 having a flanged connection 134 with the bottom of the bearing housing, and this column terminates in its lower portion in a hood 135 overhanging the impeller 136. ln order to provide for recirculation of pulp from the upper portion of the cell, holes or openings 137 are provided at the lower end of column 133, and the inilowing pulp thus passes directly into the zone of influence of the respective impellers.

The impeller 136 in cell CX has upper and lower slanting surfaces tending to converge at a point beyond the periphery of the impeller. The space between said surfaces is divided by a partition member 13S supported on suitable upstanding rods or other structure providing an the one in cell CX in that the central portion, while partitioned, is rotary instead of stationary. The entire impeller unit is located at the lower end of the shaft and has openings corresponding to the openings lill in its top surface, which openings bear the reference numeral lf3/l, similar openings in the bottom bear the reference numeral 155.

This impeller also has slanting top and bottom surfaces tending to converge beyond the periphery of the impeller and the intermediate division member M8 is arranged to extend slightly beyond the peripheral extent of the other said members. This partition divides the intcricr of the impeller into an upper chamber or Compartment 1729 and a lower compartment LSt, and gas to 'i r.tate the material treated by the impeller, is fed through lateral oper gs i532 into the upper compartment and through similar openings SB into the lower compartment. As in the former arrangement top openings l'fl ure provided to introduce pulp into the upper compartment and lower openings 155 are provided for the inte e of pulp into the lower compartment 3.5i. Also, to increase the aerating effect and di ribution of pulp, l prefer to locate a series of openings 156 in the radial blades of both the upper and lower chambers of said impeller.

ln the operation of this unit, pulp entering through feed inlet l2?. descends into the lower zone of cell CX and entrained within the enclosure formed by the support to the partitioning member L38. This pulp enters the bottom compartment through the openings M2, while other p'rlu rising in the cell enters the bottom of the column 33 through the openings 157 and descends through the top openings 1M of the impeller to enter the upper compartment of said unit. At the same time air is fed through the shaft M9 by introduction through branch E29 under the control of valve 131 nd this gas discharges through the lateral openings into the impeller enclosure. At the same time, other gas entering through a second branch descends into the column 33 to mix with the recirculating pulp so that pulp fed to the upper compartment of the impeller is a partially aerated mixture at the time it reaches said impeller.

From the foregoing description, it will be apparent that the pulp is mixed and aerated in upper and lower treatment zones and while the zones are contiguous and may be provided with an interconnecting opening at the center of the partitioning member, the action in each said zone is of a dilfercnt character. The lower zone functions primarily as a circulator, bringing in pulp from underneath the lower surface of the impeller and distributing it through the cell, whereas the upper chamber cntrains the circ 'ng pulp with only a minor amount of pulp taken in item the bottom chamber and moving into the upper chamber.

ln each of the forms thus far described there is an upper aeration zone or chamber wherein pulp from the upper portion of the cell is drawn in and subiected to further aeration and beating. The discharge from this upper aerator or chamber is in proper condition t0 elevate the coated or ilrned minerals particles into the froth bed at the surface.

ln addition, the discharge of large quantities of aerated pulp into the upper portion of the pulp body, in which the gas is widelf.I dispersed, serves to create a buoyant condition for pulp ascending from the lower impeller or pumping unit, and thus accelerates or assists the movement of coated or lmed particles from the lower impeller into the froth bed.

With this understanding of the various cell arrangements that may be utilized in the practice of the present invention, the variations in details of the structural arrangements of the lower agitator units will now be described.

As shown in Figs. l, 2 and 3, these rotors or agitators are of the squirrel-cage type, preferably having central top and bottom openings through which pulp is admitted or drawn for beating and agitation within the squirrelcage structure.

ln preferred practice, it will be desirable to utilize the pumping effect of these agitators to draw pulp interiorly of the unit from the bottom of the cell. Such pulp usually contains a considerable quantity of solids which do not remain in suspension and which are not tending to tloat.

Since some of these solids comprise the material concentrated, flotation can be induced either by aeration alone Or aeration plus mixing with additional reagent. Therefore it is advantageous to have the bars or blades comprising the side pieces or blades of the squirrel-cage assembly inclined from the vertical se as to impart upward component of movement to matet acted on by such blades. To this end the squirrel cage structure may comprise two sections arranged as upper and lower sections and suitably joined as by bolts, welding or the like with the ends of the bars of one set `n s' perposed relation to the ends of the bars of the other set; or unitary structure may be provided in which the bars extend from the top plate or disk to the bottom plate or disk of the squirrel-cage assembly.

Figs. 5 and 8 illustrate an arrangement in which the blades of the upper section are inclined to impart an upward component of movement while the blades of the lower section impart a downward component.

ln such arrangement the agitator will exert a sweepf ing action on the bottom of the cell and would preferably be used where the material under treatment is readily loated or at least remains in suspension under the agitative influence.

ln the arrangement shown in Figs. 6 and 9, the blades of the lower section are inclined to impart an upward component, and the blades f the upper section impart a downward component. This arrangement is preferable when a considerable degree of mixing is required within the agitator unit as the entering streams of pulp are caused to converge and tend to intersect when discharged across the periphery of the unit.

The arrangement shown in Figs. 7 and l0 is a preferred arrangement when portions of the pulp tend to settle and remain out of suspension. The entire blade ucture is utilized in producing an elevating component and considerable mixing is obtained due to the intake of pulp through the vortex forming at the top opening. ln addition, large quantities of pulp will be drawn in through the bottom opening rnd all of the entering pulp turns upwardly and outwardly in the ensuing agitation.

.ln all the arrangements hereinbefore described, the lower unit functions primarily as an agitator to produce the desired degree of circulation and to maintain the solids in suspension. At the same time the upper unit is functioning primarily as an aerator and is utilized in the re-treatment of the portion of the pulp tending to float but which does not pass into and remain in the froth body at the surface. Selective control of the aeration is provided in al] these arrangements both by the size of opening from the shaft to the respective impeller units and also through the valve controlled gas introduction through the hollow column or encasing structure by which the aerating gas is supplied to the upper aerating unit through premixing with the recirculating pulp.

As a result of these arrangements two (2) distinct zones of treatment are provided at different elevations within each cell or treatment stage. The lower treatment zone provides the required circulation and the necessary suspension of the solids content `while the upper zone acts as a dotation or aerating booster to provide the dispersion of gas and the solids elevating component required in the treatment. Each unit is thus permitted to function at maximum efficiency and maximum overall eiiiciency is obtained, in contrast to the action of a single rotor which has to be operated either for maximum circulating efficiency or maximum aerating efficiency but which cannot provide both.

While a hollow shaft construction has been illustrated, it will be desirable to cap either end or both for certain operations. When gas under pressure is delivered into the shaft through the bearing housing, the upper end will be capped as indicated in the cell C of Fig. 1.

When aeration on the underside of the lower impeller is not required, the bottom opening of the shaft may be capped and this will be particularly desirable when the upper end is open and atmospheric air is being drawn through said shaft. Also in some treatments, it will be desirable to .utilize gas of different compositions in the aerating action. In Fig. l, for example, compressed air would be delivered through the header 2,3 into branch 29 and down the hollow shaft while the branch 38 would be supplied from a second header (not shown) and might be CO2 for example.

The practice of the invention has been illustrated as applicable to froth flotation treatments for which it is well suited. But it is to be understood that the features of this invention may be utilized in various agitating and conditioning treatments in ore milling, paper treatment, chemical industries and the like.

What is claimed is:

l. Apparatus for agitating and aerating solids in liquids, comprising a tank for pulp having a feed inlet and a discharge outlet determining a liquid level therein, a hollow shaft journaled for rotation in the tank and having its lower end spaced from the bottom of said tank, at least two impeller members mounted on said shaft for conjoint rotation at different elevations in the pulp body, a stationary enclosure overhanging an upper impeller and having a central opening for recirculation of pulp through the space between said impeller and its enclosure, there being a bottom opening for delivery of pulp to the lower impeller under its pumping influence, there being vertically spaced openings in the shaft for discharging an aerating gas into the path of rotation of each impeller, means for delivering gas under pressure through said hollow shaft, and means for rotating said impeller members.

2. Apparatus for agitating and aerating solids in liquids, comprising a tank for pulp having a feed inlet and a discharge outlet determining a liquid level therein, a hollow shaft journaled for rotation in the tank and having its lower end spaced from the bottom of said tank, at least two impeller members mounted on said shaft for conjoint rotation at different elevations in the pulp body, a stationary enclosure overhanging an upper impeller and having a central opening for recirculation of pulp through the space between said impeller and its enclosure, there being a bottom opening for delivery of pulp to the lower impeller under its pumping influence, there being vertically spaced openings in the shaft for discharging an aerating gas into the path of rotation of each impeller, means for delivering gas under pressure through said hollow shaft, means for rotating said impeller members, and means associated with the lower impeller for breaking up the pulp streams moving under the impelling influence of said impeller.

3. Apparatus for agitating and aerating solids in liquids, comprising a tank for pulp having a feed inlet and a discharge outlet determining a liquid level therein, a hollow shaft journaled for rotation in the tank and having its lower end spaced from the bottom of said tank, at least two impeller members mounted on said shaft for conjoint rotation at different elevations in the pulp body, a stationary enclosure overhanging an upper impeller and having a central opening for recirculation of pulp through the space between said impeller and its enclosure, there being a bottom opening for delivery of pulp to the lower impeller under its pumping influence, there being vertically spaced openings in the shaft for discharging an aerating gas into the path of rotation of each impeller, means for delivering gas under pressure through said hollow shaft, means for rotating said irnpeller members, and means comprising an apertured enclosure extending around the lower impeller member for breaking up the pulp streams moving under the impelling influence of said impeller.

4. Apparatus for agitating and aerating solids in liquids, comprising a tank for pulp having a feed inlet and a discharge outlet determining a liquid level therein, a hollow shaft journaled for rotation in the tank and having its lower end spaced from the bottom of said tank, at least two impeller members mounted on said shaft for conjoint rotation at different elevations in the pulp body, a stationary enclosure overhanging an upper impeller and having a central opening for recirculation of pulp through the space between said impeller and its enclosure, there being a bottom opening for delivery of pulp to the lower impeller under its pumping influence, there being vertically spaced openings in the shaft for discharging an aerating gas into the path of rotation of each impeller, means for delivering gas under pressure through said hollow shaft, means for rotating said impeller members, and means comprising an apertured annular enclosure extending around the lower impeller member for breaking Aup the pulp streams moving under the impelling influence of said impeller.

5. Apparatus for agitating and aerating solids in liquids, comprising a tank for pulp having a feed inlet and a discharge outlet determining a liquid level therein, a hollow shaft journaled for rotation in the tank and having its lower end spaced from the bottom of said tank, a hollow column sealed from the atmosphere and extending into the pulp body in surrounding relation to said shaft, a hood member carried at the lower end of the column in open communication therewith, a rotary impeller mounted on the shaft immediately under the hood, a lower squirrel-cage impeller on the shaft having top and bottom intake openings, there being a plurality of openings in said shaft for the delivery of aerating gas onto each of said impellers, an annular apertured enclosure for said lower impeller spaced from and in proximity to the periphery of the impeller, means for delivering gas under pressure into the hollow column, means for delivering gas under pressure through said shaft, and means for rotating said shaft.

6. Apparatus for agitating and aerating solids in liquids, comprising a tank for pulp having a feed inlet and a discharge outlet determining a liquid level therein, a hollow shaft journaled for rotation in the tank and having its lower end spaced from the bottom of said tank, a hollow column sealed from the atmosphere and extending into the pulp body in surrounding relation to said shaft, a hood member carried at the lower end of the column in open communication therewith, a rotary impeller mounted on the shaft immediately under the hood, a lower squirrelcage impeller on the shaft having top and bottom intake openings, there being a plurality of openings in said shaft for the delivery of aerating gas onto each of said impellers, an annular apertured enclosure for said lower impeller spaced from and in proximity to the periphery of the impeller, there being at least one opening in the column for recirculating pulp from the cell onto the upper impeller, means for delivering gas under pressure into the hollow column, means for delivering gas under pressure through said shaft, and means for rotating said shaft.

7. Apparatus for agitating and aerating solids in liquids, comprising a tank for pulp having a feed inlet and a discharge outlet determining a liquid level therein, a hollow shaft journaled for rotation in the tank and having its lower end spaced from the bottom of said tank, a hollow column sealed from the atmosphere and extending into the pulp body in surrounding relation to said shaft, a hood member carried at the lower end of the column in open communication therewith, a rotary impeller mounted on the shaft immediately under the hood, a lower squirrelcage impeller on the shaft having top and bottom intake openings, and having the upright cage members inclined to the vertical to impart an upward component to pulp entering through s( id openings, there being a plurality of openings in said shaft for the delivery of aerating gas onto each of said impellers, an annular apertured enclosure for said lower impeller spaced from and in proximity to the periphery of the impeller, means for delivering as under pressure into the hollow column, for denverstg ,cas under pressure through said shaft, and means for rotating said shaft.

8. Apparatus for agitating and aerating solids in liquids, comprising a tank for pulp having a feed inlet and a discharge outlet determining a liquid level therein, a hollow shaft journaled for rotation in the tank and having its lower end spaced from the bottom of said tank, a hollow column sealed from the atmosphere and cxtending into the pulp body in surrounding relation to said shaft, a hood member carried at the lower end of the column in open communication therewith, a rotary impeller mounted on the shaft immediately under the hood, a lower squirrel-cage impeller on the shaft having top and bottom intake openings, and having the upright cagemembers inclined to the vertical to impart a downward component to pulp entering through said openings, there being a plurality of openings in said shaft for the delivery of aerating gas onto each of said impellers, an annular apertured enclosure for said lower impeller spaced from and in proximity to the periphery of the impeller, means for delivering gas under pressure into the hollow column, means for delivering gas under pressure through said sha t, and means for rotating said shaft.

9. Apparatus for agitating and aerating solids in liquids, comprising a tank for pulp having a feed inlet and a discharge outlet determining a liquid level therein, a tollow shaft journaled for rotation in the tank and having its lower end spaced from the bottom of said tank, a hollow column sealed from the atmosphere and extending into the pulp body in surrounding relation to said shaft, a hood member carried at the lower end of the column in open communication therewith, a rotary impeller mounted on the shaft immediately under the hood, a lower squirrel-cage impeller on the shaft having top and bottom intake openings, and having the upright cage members inclined to the vertical to impart both upward and downward components to pulp entering through said openings, there being a plurality of openings in said shaft for the delivery of aerating gas onto each of impellers. an annular apertured enclosure for said lower impeller spaced from and in proximity to the periphery of the iinpeller. means for deliveringr gas under pressure into the hollow column, means for deliverina nas under pressure through said shaft, and means for rota ing said shaft.

l0. ln aeration apparatus, including a treatment cell having a feed inlet for pulp at one end and a discharge outlet at its opposite end determining a liquid level in the cell, at least two rotary shafts extending into the pulp body in the cell at intervals spaced lengthwise of the cell between said inlet and said outlet, an upper aeratiug unit and a lower agitator unit on each shaft, conductive means for delivering an aerating gas into each said unit, and an inclined baille extending across the cell and having its top surface above and in proximity to the path of discharge flow from the upstream agitator unit and having its lowermost surface at the approximate elevation of the bottom of the downstream agitator unit and in the path of discharge flow therefrom.

ll. ln aeration apparatus, including a treatment cell having a feed inlet for pulp at one end and a discharge outlet at its opposite end determining a liquid level in the cell, at least two rotary shafts extending into the pulp body in the cell at intervals spaced lengthwise of the cell between said inlet and said outlet, an upper aerating unit and a lower agitator unit on each shaft, conductive means t'Ja (lll

for delivering an aerating gas into each said unit, a bafe disposed transversely to the direction of flow and extending between the cell bottom and the under surface of the downstream agitator centrally thereof in closely spaced relation to said under surface.

l2. ln aeration apparatus, including a treatment cell having a feed inlet for pulp at one end and a discharge ouuet at its opposite end determining a liquid level in the cell, at least two rotary shafts extending into the pulp Jody in the cell at intervals spaced lengthwise of the cell between said inlet and said outlet, an upper aerating unit and a lower agitator unit on each shaft, conductive means for delivering an aerating gas into each said unit, an inclined baille extending across the cell and having its top surface above and in proximity to the path of disch -3 flow from the upstream agitator unit and having iL lower .lost surface at the approximate elevation of the `ttom of the downstream agitator unit and in the path of discharge flow therefrom, a baille disposed transversely to the direction of fiow and extending between thc cell bottom and the under surface of the downstream a itator centrally thereof in closely spaced relation to sai Inder surface.

lfl. Apparatus for agitating and acrating solids in liti-u comprising a tank for pulp having a feed inlet and dissnarge outlet determining a liquid level therein, a hollenl s aft journaled for rotation in the tank and having its lower end spaced from the bottom of said ta .1, an aerator unit mounted for rotation on the shaft with its top surface adjacent but below the liquid level lprimis-inf.; upper and lower bladed impellers and sally aportar-ed disc between said impellers in closely spaced relation thereto, at least one impeller har/.nef a centrally disposed opening for the intake of ed pulp from the upper portion of the pulp body ia the tank, a lower squirrel-cage agitator on the shaft having top and bottom intake openings, an annular apertured enclosure for said lower agitator spaced from and in proximity to its periphery, conductive means for delivering aerating gas into said aeration and agitator units, and moans for rotating said shaft.

14. Structure as defined in claim 13, in which tle upper aerator unit has a downwardly dished surface and the lower aerator unit has an upwardly dished surface.

i5. Structure as defined in claim 13, in which the upper and lower impellers of the aerator unit are rotary fs--r el..

and 'ne disc which separates said members is stationary'.

l5. The aerating method which comprises the treatment of a body of pulp of substantial depth in a cond zone subject to continuous feed and discharge, subi pulp in lower portion of said zone to agitation I aeration within a zone of centrifugal influence into which the pulp is drawn, subjecting the aerated pulp to beatin'* action during said centifugal movement so as se the gas throughout the pulp, inducing a recircul. previously aerated pulp from an upper portion of the treatment zone into an upper zone of centrifugal influence, aerating said pulp prior to its entrance into the latter centrifugal zone, and subjecting said aerated to further aeration and agitation prior to its discharge from the upper centrifugal zone.

l7. An aerating method as dened in claim 16, in which the rate of centrifugal movement in the upper and lower centrifugal zones is uniform.

l8. ln aerating apparatus, in which pulp at different levels within a treatment tank is subjected to agitation and aerating influences, the improvement which comprises a rotary aerator having a hollow interior divided into upper and lower treatment chambers, there being a central top opening in said aerator for the intake of pulp in the upper chamber, a central bottom opening for the intake of pulp in the lower chamber, conduit means for discharging an aerating gas into each said chamber, and a foraminate partition member dividing 13 said chambers and having opening means therethrough for the passage of pulp from one chamber to the other.

19. Structure as defined in claim 18, in which the partition member is stationary and the remainder of the aerator is rotary.

References Cited in the le of this patent UNITED STATES PATENTS 1,283,159 Groch Oct. 29, 1918 

1. APPARATUS FOR AGITATING AND AERATING SOLIDS IN LIQUIDS, COMPRISING A TANK FOR PULP HAVING A FEED INLET AND A DISCHARGE OUTLET DETERMINING A LIQUID LEVEL THEREIN, A HOLLOW SHAFT JOURNALED FOR ROTATION IN THE TANK AND HAVING ITS LOWER END SPACED FROM THE BOTTOM OF SAID TANK, AT LEAST TWO IMPELLER MEMBERS MOUNTED ON SAID SHAFT FOR CONJOINT ROTATION AT DIFFERENT ELEVATION IN THE PULP BODY, A STATIONARY ENCLOSURE OVERHANGING AN UPPER IMPELLER AND HAVING A CENTRAL OPENING FOR RECIRCULATION OF PULP THROUGH THE SPACE BETWEEN SAID IMPELLER AND ITS ENCLOSURE, THERE BEING A BOTTOM OPENING FOR DELIVERY OF PULP TO THE LOWER IMPELLER UNDER ITS PUMPING INFLUENCE, THERE BEING VERTICALLY SPACED OPENINGS IN THE SHAFT FOR DISCHARGING AN AERATING GAS INTO THE PATH OF ROTATION OF EACH IMPELLER, MEANS FOR DELIVERING GAS UNDER PRESSURE THROUGH SAID HOLLOW SHAFT, AND MEANS FOR ROTATING SAID IMPELLER MEMBERS. 